In manufacturing a large-scale integration (LSI), tungsten has been widely used for MOSFET gate electrodes, source-drain contacts, memory wordlines and the like. A Cu wiring has been mainly used in a multilayer wiring process. However, Cu has a poor heat resistance and is easily diffused. As such, tungsten has been used for a portion that requires a heat resistance or a portion of which an electric property may deteriorate due to the diffusion of Cu.
A physical vapor deposition (PVD) method has been used as a film forming process of a tungsten film. However, it is difficult to use such a PVD method for a portion that requires a high coverage rate (step coverage). Because of this, a chemical vapor deposition (CVD) method which provides good step coverage has been performed to form the tungsten film.
As a method of forming a tungsten film (CVD-tungsten film) using such a CVD method, a method of inducing a reaction of WF6+3H2→W+6HF on a semiconductor wafer as a target substrate, by using a tungsten hexafluoride (WF6) as a raw material gas and an H2 gas as a reduction gas, is generally used.
However, when the tungsten film is formed by the CVD method using the WF6 gas, fluorine contained in WF6 reduces a gate insulation film in a semiconductor device, particularly in gate electrodes, memory wordlines or the like, which deteriorates an electric property of the semiconductor device.
As a raw material gas used in forming a CVD-tungsten film containing no fluorine, tungsten hexachloride (WCl6) is known. Although chlorine has a reduction property like fluorine, reactivity of chlorine is weaker than that of fluorine. As such, chlorine is expected to hardly affect the electric property.
In recent years, as the semiconductor device becomes finer and finer, it is difficult to use the CVD method, which is known to provide good step coverage, to bury a film into a complex-shaped pattern. Thus, from the viewpoint of obtaining higher step coverage, an atomic layer deposition (ALD) method which sequentially supplies a raw material gas and a reduction gas while performing a purge process in the course of sequentially supplying the raw material gas and the reduction gas, is getting a lot of attention.
In some instances, a complex-shaped semiconductor device such as a three-dimensional (3D) NAND flash memory has been developed. Formation of a tungsten film on such a complex-shaped semiconductor device requires supplying a film-forming raw material at a high flow rate.
Meanwhile, there are generally simple flat portions such as peripheral circuits even in the complex-shaped semiconductor device. In forming a film on the device having such complex-shaped and flat portions by using a chloride such as tungsten hexachloride (WCl6) as a film-forming raw material, if the chloride raw material is supplied at a flow rate that is required to form the film on the complex-shaped portion, hardly any of the film will be formed on the flat portion.